Secondary emitter tube



May 23, 1939- G. BRAul-:R ET AL 2,159,519

- SECONDARY EMITTER TUBE Filed Feb. 17, 1937 W7 www.:

@aff/wa argue/P, 0kg/75am,

Patented May A23,1939

UNITED STATES PATENT vOFFICE SECONDARY EMITTER TUBE many Application February 17, 193.7, Serial No. 126,312 In Germany February 20, 1936 Claims.

This invention is related to secondary emission tubes in which the multiplication of electrons, emitted by a thermionic or photo-cathode occurs by impact on solid surfaces and by the secondary 5 emission taking place thereby. In most cases,

use. is made of this multiplication in several stages, whereby a very high multiplication can be obtained within one vacuum receptacle.

So far,ldevices are known, in which the secondary emitting electrode has the shape of a cylinder, surrounding an anode Wire with a collector Iplate at one end lying in the axis of the cylinder. The cylinder of high resistance material has a potential which increases from the end where the primary electrons enter towards'the end where lthe collector is placed, so that a longitudinal electric eld exists in the interior of the cylinder, Lupon which is superimposed a radial field caused by the anode wire.

2 In this known device, the primary electrons should strike the surface of the emitting electrode when enteringy and liberate secondaries. These secondaries are accelerated by the anode wire and should, to a greater part, impact the 25 opposite wall of the cylinder in order to liberate new secondaries from there. Because of the longitudinal iield, the spot of impact travels towards the end of the cylinder, Where the electrons are collected on the end plate.

30 The practical gain in such a device is however very small, because the electrons nearly all impact the anode wire and do not pass it as intended. Such a collecting effect of the anode is caused by the radial iield. However, it has not 35 been recognized so far that the device was inoperable for this reason.

According to the invention, a cylindrical anode is used instead of an anode wire, which also produces a radial eld, but is permeable for electrons, land may consist for instance of a mesh-work, sieve, grid or similar elements. Only a small part of the secondary electrons emitted are collected by the anode and the greater part passes through the anode. Thus the electrons are rst accelerated towards the anode, fly through the Faraday space in the interior of the anode, and impact the opposite wall of the emitting electrode. v

Furthermore, it is within the scope of the invention to subdivide the anode into a number of permeable accelerating electrodes, which may consist, for instance, of a number of rings or cylinders aligned in axial direc-tion, having a potential increasing from stage to stage. In such a device, it is advisable to subdivide the emitting (Cl. Z50-175) electrode also in a number of individual electrodes with increasing potential.

The drawing shows embodiments of the invention.

Figure 1 shows a view of an electron tube.

Figure 2 shows a cross-section through the tube in the plane 2 2.

Figure 3 shows a modification.

The tube contains a cathode I, for instance, a thermionic or a photo-cathode. A control electrode 2 is placed *in front of the cathode in the shape of a plane spiral which covers the opening of the adjacent emitting electrode 3.

The emitting electrode consists of a number of consecutive individual cylinders 3 to I0, the positive potential of which increases with the distance from the cathode I. The anode is also subdivided into several permeable accelerating electrodes I I to I8, also with a potential increasing from stage to stage. The accelerating electrodes, are placed within the respective emitting electrodes, but are suitably displaced in the direction of the increasing potential. The accelerating electrodes may be, for instance, connected to emitting electrodes of the same potential within the tube, such as the emitting electrode of the next stage or the one following the next. This decreases the number of necessary leads. A further decrease in the number of leads, the limit of which is two, is obtained by connecting the electrodes, by large resistances I9 in the vacuum. These resistors carry a current which is large -compared to the largest existing secondary electron current. The diameter of the permeable accelerating electrode is considerably larger than that of the anode wire used in the known device. The emitting electrodes have varying diameters and overlap in axial direction, making an impermeable envelope for the electrons.

The accelerating and emitting electrodes may consist of a high resistance layer or of a spiral of a high resistance wire or band.

The first emitting electrode has already a positive potential in respect to the control grid 2, so that the electrons controlled by the grid cause the first amplification at the emitting electrode 3. The secondary electrons traverse the space within the accelerating electrode II under the influence of the accelerating field, and arrive on the second emitting electrode 4 with great velocity. The electrode 4 may be, for instance, 400 volts more positive than the electrode 3. This procedure is repeated from stage to stage. Beyond the last anode I8 there is an end plate 22 which collects all electrons.

In the modication according to Figure 3, a photo cathode 20 of a large area is used as emitting surface for the primary electrons. This sur- -face is oblique in respect to the axis of the amplifier, so as not to obstruct the passage of light. The photo-electrons are accelerated towards the emitting electrode 3, by means of a mesh Work 2 I, which may be plane or convex in the direction of the photo-cathode. The accelerating electrodes Il to I4 consist, in this case, of short cylinders, or of individual rods which are arranged on a cylindrical surface and interconnected.

The primary electrons may also enter the amplier in the shape of an electron beam, for instance, through a foil or similar element.

What is claimed is:

1. An electron multiplier comprising an evacuated envelope having therein a primary electron source, means for modulating said source in response to a signal, and a plurality of cylindrical cathodes disposed in axial alinement With saidy primary source, said cylindrical cathodes having secondarilyremissive interior surfaces, a plurality of ring anodes disposed Within said cathodesand axially alined with said primary source, each of said ring anodes being connected to one of said cathodes disposed farther from said primary source, and a collecting anode alined with said lprimary source and said ring anodes.

2.r An lelectron multiplier comprising an evacuated envelope having therein a primary electron source, means for modulating electrons from said source in accord with a signal, a plurality of cylindrical cathodes havingy secondarily emissive interior surfaces disposed in axial alinement with said primary source, a plurality of accelerating electron permeable anodes disposed Witn- 'in said cathodes and alined With said primary source, each of said anodes being disposed at the end of the cathode with which it is associated farthest from said primary source and being connected to one of said cathodes disposed farther from said primary source, and a collecting anode alined with said cathodes.

3. An electron multiplier comprising an evacuated envelope having therein a primary electron source, means for controlling emission from said source in response to a signal, a plurality of cylindrical cathodes having secondarily emissiveV interior surfaces alined with said primary source, a, collecting anode disposed in alinement with said cathodes and said `primary source, and an electron permeable accelerating anode disposed -Within each of said cylindrical cathodes and at the end thereof farthest from said primary source, said cylindrical cathodes being alternately of greater and lesser diameter, each of said accelerating ranodes being connected to one of said cathodes farther from said primary source and adapted to direct electrons from the adjacent secondarily emissive cathode surface toward said collecting' anode.

4. An electron multiplier comprising an evacuated envelope having therein a photoelectric surface and accelerating grid, a cylindrical cathode connected to said grid and having a secondarily-emissive interior surface, a plurality of cylindrical cathodes havingy secondarily emissive interior surfaces alined with said Ygrid and said cylindrical cathode, a collecting anode ,positioned to receive electrons from said cathode surfaces,

and a plurality of accelerating electrodes disposed within said cylindrical cathodes, each of said accelerating electrodes comprising a plurality of conducting fingers disposed parallel tothe axis of said cathodes and evenly spaced about a conducting ring concentric therevvithin 5. An electron multiplier comprising an envelope having therein aprimarysource of electrons, and a plurality of cathodes disposed rin alignment with said primary source andhaving secondarily emissive surfaces, a plurality of electron permeable anodes disposed within said cathodes and in alignment with said'primary-source, each of said anodes being connected Vto one of said cathodes disposed farther from said primary source, and a collecting anode ffor collecti ing the electrons emitted from that cathode farthest from said primary source.

RICHARD BRAUER, MAGDALENE BRAUER,

NE NAUMANN, H eirs of the Estate of Gerhard .BrauenDe'ceased ERNST RUSKA. 

